The invention relates to a flowmeter having a displacement meter to which a pressure difference sensor is connected in parallel in a bypass line, wherein as a function of a differential pressure ascertained by the pressure difference sensor between the inflow side and the outflow side of the displacement meter, a motor rotatably connected to the displacement meter is controlled for constant differential pressure equalization, wherein the pressure difference sensor has a piston which is freely movable in a cylinder region of the bypass line and of which the deflection due to the occurrence of a differential pressure is determined and is used for control of the motor of the displacement meter, and wherein the bypass line has a bypass channel which frees a connection between the inflow side and the outflow side when a piston butts against a maximum stroke stop on the outflow side.